In co-pending U.S. patent application Ser. No. 32,646 entitled "The Kinetic Extruder--A Dry Pulverized Solid Material Pump", now abandoned assigned to the same assignee as the present patent application, it is noted that there are a number of industrial processes which require the feeding of particulate material from a lower atmospheric pressure environment to the elevated pressure environment within the working vessel.
The invention set forth in that patent application provides a method and apparatus for the continuous feeding of pulverized or powdered solid material such as coal to a pressurized vessel. This is achieved by the use of a rotor within a pressurized case through which the material is pumped into the vessel. The material is gas fluidized and pneumatically fed from an atmospheric feed hopper through a stationary feed pipe, then into a spin-up zone between a stationary inner hub and a rotatable driven rotor. Within the spin-up zone the material is defluidized and compacted into a packed bed as it is centrifugally driven outward and enters radial channels or sprues in the rotor. A porous compacted moving plug of material forms in the sprues and creates a seal against the high-pressure gases. The sealing action is a combined effect of both the motion of the plug and its relatively low permeability. A control nozzle structure at the distal end of the sprues stabilizes the moving material plug and controls its outward velocity to the proper value for effective sealing.
The spin-up zone is vented to a vacuum system to allow the removal of excess fluidizing gas which results from the compaction of the solids and also any small amount of gas leakage back through the compacted moving plug in the sprues from the high pressure vessel. A sub-atmospheric pressure is maintained in the spin-up zone in order to assure reliable feed from an atmospheric hopper.
In the apparatus described in the above-cited U.S. patent application Ser. No. 32,646 now abandoned the spin-up zone is an open annular area between the stationary inner hub containing the feed pipe outlet, and the plurality of the sprue inlets.
The same general spin-up zone structure is shown in U.S. Pat. No. 4,265,580 entitled "A System for Throttling and Compensating for Variable Feedstock Properties" and U.S. patent application Ser. No. 199,861, now U.S. Pat. No. 4,362,441, entitled "Means and Apparatus for Throttling a Dry Pulverized Solid Material Pump", both assigned to the same assignee as the present patent application.
It is important to recognize that the coal issuing from the feed pipe has no rotary motion, is fluidized with gas, and is of relatively low bulk density; i.e., 20-25 lbs/ft.sup.3. On the other hand, the moving coal bed within the sprues is non-fluidized and is compacted to 40-50 lbs/ft.sup.3 density, and rotates with the rotor. The spin-up zone is therefore a shear zone within which the incoming material is both accelerated to the requisite angular velocity and "settled" into a more compacted form, before entry into the sprues. The torque necessary to impart angular acceleration to the coal is applied by friction with the walls of the rotor as well as with the surface of the settled bed over the sprue inlets.
The spin-up zone of the prior applications is capable of handling a limited rate of flow of material. If the withdrawal rate through the sprues exceeds the critical value, there is insufficient spin-up and compaction of the coal and an adequate pressure sealing plug in the sprue cannot be formed. Attempts to run at higher throughputs resulted in "blowbacks" due to the loss of the integrity of the sprue plugs.